Claudine Lewis, of Boston, places flowers on a makeshift memorial in front of fire station Engine 33/Ladder 15, Thursday, in Boston. Engine 33/Ladder 15 was the station of fallen firefighters Lt. Edward Walsh and Michael Kennedy who lost their lives fighting a nine-alarm blaze in a four-story brownstone in Boston’s Back Bay neighborhood Wednesday.

BOSTON — One was a fitness enthusiast who helped the wounded after the Boston Marathon bombings and planned to run the race himself this year. The other was a father of three young children who had firefighting in his blood.

The smoke from a wind-whipped fire had dissipated Thursday, but a palpable sadness hung over the city as tributes poured in for Michael Kennedy and Edward Walsh, the two firefighters who died after becoming trapped in a basement in a brownstone apartment building.

The cause of Wednesday’s fire, which also sent more than a dozen other firefighters and several police officers to hospitals, was unknown. Steve MacDonald, a fire department spokesman, said a conclusion could be months away.

Outside Engine 33/Ladder 15, the station where Walsh and Kennedy worked, people stopped to pay their respects, some crying, others praying. Flowers were draped on the fire alarm outside the brick building and piles of boutiques accumulated.

Firefighters continued their work.

“Life goes on,” Dennis Costin said as alarms went off at the station. “It’s all we can do.”

Kennedy, 33, joined the U.S. Marine Corps in 2001 and was on active duty for six years, including a deployment to Iraq, before joining the fire department in 2007.

In April, he was among the first responders to the twin bombings at the Boston Marathon finish line, just a few blocks from the station.

“He was devastated by it. He told us about helping to hold someone together, someone with bad injuries,” said Shelley White, the general manager of Personalized Fitness, a health and wellness center where Kennedy also worked as a coach in the CrossFit Together program.

Kennedy wrote an essay to earn a spot in the marathon this year and had been training with other firefighters planning to run in the April 21 race, said Gov. Deval Patrick, who was among those who stopped by the station Thursday.

Walsh, whose three children are all younger than 10, was a devoted family man who was physically imposing yet reserved, friends said.

“He wasn’t one of these rah-rah guys, but he just had a presence about him,” said John Tobin, a Northeastern University administrator who lives a few streets from Walsh’s family in the city’s West Roxbury neighborhood.

Tobin’s son, Matthew, and Walsh’s son, Dylan, were friends and classmates at Holy Name Parish school, where they played on a basketball team together. On Sunday, Walsh and Tobin engaged in a friendly but vigorous father-child game on the court.

“We were joking about who was going to blow out his ACL first,” said Tobin.

But Tobin never heard the tall, fit Walsh talk about the dangers of his profession.

“It didn’t appear from the look of him that Ed was scared of much,” said Tobin.

Walsh, 43, grew up in Watertown, part of a family of firefighters. His late father and two uncles were firefighters in that Boston suburb, and a cousin and brother-in-law currently serve in the department.

The fire in the Back Bay neighborhood broke out mid-afternoon as an offshore storm lashed the city with strong winds, causing the flames to spread quickly, officials said.